DESCRIPTION: One percent of newborn humans have some congenital heart defect, usually in the septation of the heart. Despite this medical importance, little is known about the molecular bases for the cellular processes that convert the heart from an undifferentiated mass of cells to a single straight tube and then to a four-chambered structure. These changes results from a series of epithelial-mesenchymal transformations wherein epithelial cells in sheets lose adhesion , convert to migrating mesenchymal cells, and finally differentiate in spatially and temporally regulated patterns into novel structures. The long-term objective of these studies is to identify the specific molecules involved in this regulation of cellular adhesion and how these adhesion molecules affect cell behavior. To this end, recent studies have focussed on a class of extracellular matrix proteins, large extracellular chondroitin sulfate proteoglycans (CSPGs), as well on cell-surface receptors for these CSPGs. the proposed experiments focus on the observation that the interaction of the CSPG neurocan with the cell surface glycosyltransferaseN-acetylgalactosaminylphosphotransferase (GalNAcPTase) initiates a signal transduction cascade that indirectly inhibits the function of the cell-cell adhesion molecule N-cadherin. A variety of evidence suggests the hypothesis that this interaction may regulate the de-adhesion and subsequent cell migration and differentiation that occurs during one of the epithelial-mesenchymal transformations that are critical in heart development. In order to test this hypothesis, the following specific aims will be performed: 1) Determine the specific polypeptide sequences or oligosaccharides in neurocan involved in its interaction with GalNAcPTase, and 2) Determine the consequences of neurocan-GalNAcPTase interactions on the de-adhesion, cell migration, and differentiation that occur during epithelial-mesenchymal transformations in early heart development and on signal transduction mechanisms involving protein tyrosine phosphorylation. These experiments will use a variety of cell biological, molecular biological, biochemical, and immunological methods. Potential health benefits of these studies are the ability to recognize and understand the molecular bases of congenital heart defects and to design strategies to correct these defects.